Messages in this thread | | | From | Dan Williams <> | Date | Wed, 15 Jan 2020 22:05:00 -0800 | Subject | Re: [RFC PATCH V2 01/12] fs/stat: Define DAX statx attribute |
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On Wed, Jan 15, 2020 at 9:39 PM Darrick J. Wong <darrick.wong@oracle.com> wrote: [..] > > attempts to minimize software cache effects for both I/O and > > memory mappings of this file. It requires a file system which > > has been configured to support DAX. > > > > DAX generally assumes all accesses are via cpu load / store > > instructions which can minimize overhead for small accesses, but > > may adversely affect cpu utilization for large transfers. > > > > File I/O is done directly to/from user-space buffers and memory > > mapped I/O may be performed with direct memory mappings that > > bypass kernel page cache. > > > > While the DAX property tends to result in data being transferred > > synchronously, it does not give the same guarantees of > > synchronous I/O where data and the necessary metadata are > > transferred together. > > (I'm frankly not sure that synchronous I/O actually guarantees that the > metadata has hit stable storage...)
Oh? That text was motivated by the open(2) man page description of O_SYNC.
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